They do work – the o-ring keeps the lock-ring positioned on the die body, but:

Cons

The o-ring doesn’t firmly keep the lock-ring positioned on the die body; it’s easy to bump out of place, and then you have to reset your die.

Dillon

Pros

this simple, compact lock ring works fine on a Dillon or other progressive die-plate, because it’s set-and-forget. The die never leaves the plate. The compactness of the Dillon lock-ring makes it easier to get a tool on.

Cons

Once the die is removed you need to reset it – it has no feature to secure it in position on a die. Suited only to a progressive die-plate.

And there you have it. A simple think like a lock ring can make your life better, or make it more frustrating.

More Pics

Redding lock ring – notice the outer set screw and inner thread-fitting lock piece. That makes it the best of the set-screw types – although Redding has no wrench flats.

Here’s the Dillon. It’s just a nicely-coated locknut, and works perfectly for it’s intended purpose of keeping a die in a die plate.

And the Lee. The o-ring tends to keep the ring from self-adjusting. Once tightened down, the o-ring compresses and acts to stop the die from turning. But there are better ways, as above.